Extractive Bioconversion of 2-Phenylethanol from L-Phenylalanine by Saccharomyces cerevisiae

The bioconversion of L-phenylalanine (L-Phe) to 2-phenylethanol (PEA) by the yeast Saccharomyces cerevisiae is limited by the toxicity of the product. PEA extn. by a sep. org. phase in the fermenter is the ideal in situ product recovery (ISPR) technique to enhance productivity. Oleic acid was chosen as org. phase for two-phase fed-batch cultures, although it interfered to some extent with yeast viability. There was a synergistic inhibitory impact toward S. cerevisiae in the presence of PEA, and therefore a maximal PEA concn. in the aq. phase of only 2.1 g/L was achieved, compared to 3.8 g/L for a normal fed-batch culture. However, the overall PEA concn. in the fermenter was increased to 12.6 g/L, because the PEA concn. in the oleic phase attained a value of 24 g/L. Thus, an av. volumetric PEA prodn. rate of 0.26 g/L-h and a maximal volumetric PEA prodn. rate of 0.47 g/L-h were achieved in the two-phase fed-batch culture. As ethanol inhibition had to be avoided, the prodn. rates were limited by the intrinsic oxidative capacity of S. cerevisiae. In addn., the high viscosity of the two-phase system lowered the kla, and therefore also the productivity. Thus, if a specific ISPR technique is planned, it consequently has to be remembered that the productivity of this bioconversion process is also quickly limited by the kla of the fermenter at high cell densities. [on SciFinder (R)]